Vasicola Pv Research Articles

In vitro inhibition of Xanthomonas vasicola pv. musacearum, the causal agent of banana Xanthomonas Wilt, using medicinal plant extracts from North Kivu, Eastern Democratic Republic of Congo

Banana Wilt caused by Xanthomonas vasicola pv. musacearum (Xvm), has emerged as a significant threat to food security in eastern Democratic Republic of Congo (Kivu). Currently, the only means of combatting this biotic constraint is through best agricultural practices. The aim of this study was to evaluate the effectiveness of medicinal plants used in the Kivu provinces in inhibiting Xvm. Three in vitro experiments were conducted at laboratories of Uganda's National Agriculture Research Organization (NARO) and the International Institute of Tropical Agriculture (IITA) in South Kivu. The bacterial samples were collected from infected field-grown banana plants in South Kivu and isolated on Yeast Extract Peptone Agar (YPGA). Pure Xvm colonies were used for identification via i) Polymerase Chain Reaction (PCR) with specific primers and, ii) greenhouse inoculation trials. A completely randomized design was used for the three inhibition tests (1) on Mueller Hinton Agar (MHA) using disc diffusion with 10 plant extracts; (2) in liquid YPG Broth using 10 plant extracts; and (3) on MHA using disc diffusion with 19 plant extracts. The first two trials used plant extracts diluted in petroleum ether, while the third trial used 19 plant extracts diluted in methanol. After maceration, filtration, and solvent evaporation, 10 mg of extract was diluted in 80 µl of distilled water + 10 µl of Dimethylsulfoxide (DMSO). Ten µl of this solution was impregnated on perforated discs of Whatman filter paper. Zingiber officinale (ginger) and Ricinus communis (castor) were the most effective plant extracts in suppressing Xvm. Of the thirteen plant species identified as effective against the pathogen, the Myrtaceae and Euphorbiaceae families were the most represented. Based on these results, evaluating the effectiveness of the most promising plant extracts in disinfecting the metal blades of garden tools is recommended. In addition, various phytochemical groups present in plant extracts could be evaluated for their effectiveness in suppressing Xvm, especially phenols and tannins.

Novel Strain Bacillus velezensis LAFUEL 03: Activity Against Xanthomonas vasicola pv. vasculorum, Control of Bacterial Leaf Streak of Corn and Genome Insights into Its Antagonistic Activity

The main objective of this study was to investigate the antimicrobial activity of three putative antagonist bacterial strains of Bacillus spp. against Xanthomonas vasicola pv. vasculorum (Xvv) and their potential to control bacterial leaf streak (BLS) of corn. Additionally, the study included investigations on the genome of one of these antagonist bacteria, such as genome sequencing and mining of genes involved in biofilm formation, swarming motility, and synthesis of secondary metabolites. The growth of Xvv was inhibited by both cell suspensions and cell-free supernatants of the bacterial strains LAFUEL 01, LAFUEL 02, and LAFUEL 03 in agar diffusion tests. All three antagonist strains significantly reduced the severity of BLS in the 3rd and 4th leaves of corn plants that were artificially inoculated at the V3 growth stage under greenhouse conditions. The 16S rRNA sequencing confirmed that the antagonistic bacterial strains belong to the genus Bacillus, with LAFUEL 03 having approximately 97% similarity to B. velezensis. B. velezensis LAFUEL 03 harbors genes related to the biosynthesis of secondary metabolites, biofilm formation/regulation, and swarming motility that enhances its potential for controlling BLS in corn and suggests a promising candidate for the development of a commercial biocontrol agent.

Effects of Hybrids, Foliar Treatments, and Infection Conditions on Bacterial Leaf Streak of Sweet Corn.

Bacterial leaf streak (BLS) of corn caused by Xanthomonas vasicola pv. vasculorum was first reported in the United States in 2017. The biology and management of BLS are poorly understood. The objective of this work was to determine the effects of hybrids, foliar treatments, and infection conditions (timing, temperature, and inoculation site) on BLS of sweet corn. Field studies were conducted to determine if hybrid or foliar disease management treatments influenced BLS development and yield. Corn leaves were inoculated in plots with X. vasicola pv. vasculorum, and noninoculated plots were used for comparison. The leaf incidence and severity of BLS differed significantly among sweet corn hybrids, suggesting different levels of susceptibility to BLS. Grain yield was significantly reduced (14.7%) by BLS for one hybrid. The corn growth stage at the time of infection influenced BLS, with incidence and severity significantly greater after inoculation at stage V6 than at V9. Foliar application of Kocide, LifeGard, and Kocide and LifeGard significantly reduced leaf severity compared with nontreated controls in field studies. Kocide significantly reduced leaf incidence, but no treatments significantly increased yield versus controls. In comparisons of inoculation methods in a growth chamber, lesion length on leaves was significantly greater on stalk-inoculated than leaf-inoculated plants. Lesions developed on leaf-inoculated plants only at inoculation sites, whereas lesions developed on stalk-inoculated plants on multiple leaves. In controlled environments, lesion length on leaves was significantly greater at 21°C than at 27 and 32°C. This study expands our understanding of factors that influence the development and management of BLS of sweet corn.

Antimicrobial and Molecular Docking Studies of Anthrones from the Leaf Latex of Aloe pirottae A. Berger against Some Plant Pathogenic Microbes

Objective/Background: Aloe pirottae A. Berger has traditionally been used in Ethiopia to treat various ailments. While previous studies have examined the antimicrobial activity of different parts of A. pirottae against human pathogens, this study aimed to investigate whether its antimicrobial activity extends to plant pathogenic bacteria and fungi. Methods: Compounds were isolated from the leaf latex of A. pirottae using silica gel column chromatography, and their structures were determined using 1H-NMR, 13C-NMR, and ESI-MS spectral data. Both the leaf latex and the isolated compounds were evaluated for their antimicrobial activity against three bacterial ( Pseudomonas syringae pv. gaarcae, Ralstonia solanacearum and Xanthomonas vasicola pv. musacearum) and three fungal ( Fusarium graminarum, Fusaium oxysporum, and Fusarium solani) plant pathogens. Results: A mixture of two diastereoisomeric anthrones was isolated from the leaf latex of A. pirottae and characterized as aloin A/B using 1H-NMR, 13C-NMR, and ESI-MS. Aloin A/B showed the most potent activity against X. vasicola among the bacteria and F. oxysporum among the fungi strains tested, with minimum inhibitory concentrations (MIC) of 3.12 mg/mL and 6.25 mg/mL, respectively. Further exploration uncovered strong binding affinity of aloin A/B towards key proteins in these pathogens, specifically with topoisomerase II (−10.060 kcal/mol) and UDP-N-acetylmuramoyl-L-alanyl-D-glutamate-2, 6-diaminopimelate ligase (murE) (−8.861 kcal/mol) in F. oxysporum and X. vasicola, respectively, through molecular docking studies. Conclusion: The present findings highlight aloin A/B as promising natural antimicrobial agents and lead compounds for new plant pathogen treatments. Further research is recommended to explore their activity against a wider range of plant pathogens.

Survival of Xanthomonas vasicola pv. vasculorum in Soil and in Corn Crop Residues under the Humid Subtropical Climate of Southern Brazil.

Bacterial leaf streak caused by Xanthomonas vasicola pv. vasculorum (Xvv) is an emerging disease in several corn-producing regions around the world. In Brazil, there is a lack of information on the survival of this bacterium in soil and crop residues. Thus, the objective of this study was to determine the survival of Xvv in soil and also in infected corn crop residues under the humid subtropical climate of southern Brazil. The survival of Xvv in soil was initially investigated in sandy and clayey soils maintained at 20, 25 and 30 °C under controlled conditions. The survival of the bacterium under field conditions was studied in artificially infested clayey soil. The survival of Xvv in corn crop residues was investigated in infected residues maintained on the soil surface or buried in the soil at 20 cm deep. Under controlled conditions, regardless of the type of soil, the bacterium survived longer at 20 °C than at higher temperatures. The bacterium survived for 40 days in clayey soil kept at 20 °C and four days in sandy soil maintained at 30 °C. Under field conditions, the survival of Xvv in the soil was only for 48 h and in infected corn crop residues for up to 15 days in the samples maintained on the soil surface. In samples of infected corn residues buried in the soil, the bacterium was only detected at the time the experiment was set up. In general, the results obtained in this study revealed that Xvv survives for a short period of time in soil and in infected corn crop residues under humid subtropical conditions. Therefore, soil and corn residues may not be highly important sources of primary inoculum for the development of bacterial leaf streak on corn crops under these conditions.

Identification of the Loci Associated with Resistance to Banana Xanthomonas Wilt (Xanthomonas vasicola pv. musacearum) Using DArTSeq Markers and Continuous Mapping

Banana Xanthomonas wilt, caused by Xanthomonas vasicola pv. musacearum (Xvm), is a devastating disease that results in total yield loss of affected plants. Resistance to the disease is limited in Musa acuminata, but it has been identified so far in the zebrina subspecies. This study identified markers associated with tolerance to Xvm in Monyet, a tetraploid banana from the zebrina subspecies which was identified to be partially resistant to the bacterium. We used a triploid progeny of 135 F1 hybrids resulting from a cross between Monyet (Xvm partially resistant) and Kokopo (diploid and Xvm susceptible). The F1 hybrids were screened in pots for resistance to Xvm. The population was genotyped using the genotyping-by-sequencing platform of Diversity Array Technology (DArTSeq). The adjusted means of the phenotypic data were combined with the allele frequencies of the genotypic data in continuous mapping. We identified 25 SNPs associated with resistance to Xvm, and these were grouped into five quantitative traits loci (QTL) on chromosomes 2, 3, 6, and 7. For each marker, we identified the favorable allele and the additive effect of replacing the reference allele with the alternative allele. The comparison between weevil borer (Cosmopolites sordidus (Germar)) and Xvm QTL revealed one QTL shared between the two biotic stresses at the distal end of chromosome 6 but with a repulsion linkage. This linkage should be broken down by generating more recombinants in the region. We also identified 18 putative alleles in the vicinity of the SNPs associated with resistance to Xvm. Among the 18 putative genes, two particularly putative genes, namely, Ma06_g13550 and Ma06_g36840, are most likely linked to disease resistance. This study is a basis for marker-assisted selection to improve banana resistance to banana Xanthomonas wilt, especially in East and Central Africa where the disease is still devastating the crop.

Dickeya zeae, Pantoea ananatis e Xanthomonas vasicola pv. vasculorum: Controle com o uso de nanopartículas

ABSTRACT Metal oxide nanoparticles (NPs) possess antibacterial activities and can be used for the control of phytopathogenic bacteria. The objective of this work was to evaluate the antibacterial activity of pure and doped NPs against Dickeya zeae, Pantoea ananatis, and Xanthomonas vasicola pv. vasculorum in vitro, and to assess the efficacy of preventive and curative application of zinc oxide (ZnO), nickel oxide (NiO), and silver-doped zinc oxide (ZnO:Ag) NPs for the control of white spot (WS) and bacterial leaf streak (BLS) in vivo. Bacterial growth inhibition was first evaluated by measuring the diameter of the inhibition zone formed in Petri dishes. Subsequently, the severity of WS and BLS diseases was evaluated in a greenhouse calculating the area under the disease progress curve. The in vitro antibacterial activity was not influenced by the increase in the concentration of doping elements for most NPs. ZnO NPs doped with Ag, K, and Mo; ZnOCl doped with Ag, and pure NPs (Ag2O, CuO, and NiO) showed antibacterial activity against D. zeae, P. ananatis, and X. vasicola pv. vasculorum with relatively similar inhibition zones at different concentrations. Commercial copper showed antibacterial activity only against D. zeae. NiO NPs in preventive and curative applications reduced WS and BLS severities, whereas commercial copper application increased WS severity and reduced BLS severity. The use of NPs has promising applications and further evaluation of their formulation, application form, and timing is necessary for new strategies to control the activity of phytopathogenic bacteria.

Reação de linhagens de milho à estria bacteriana

Abstract The objective of this work was to select experimental corn lines genetically resistant to the bacterial leaf streak caused by Xanthomonas vasicola pv. vasculorum, in two growing seasons. The treatments were carried out in an experimental randomized block design in the 2019/2020 and 2020/2021 growing seasons, under a covered environment, with open ventilation, with four replicates. Seven lines resistant to and seven susceptible to foliar diseases were evaluated, in addition to two commercial hybrids used as checks. At the corn flowering stage, an artificial inoculation containing 3.78x1010 CFU mL−1 of bacterial suspension was performed, and disease incidence and severity were assessed, based on a diagrammatic scale, every seven days. From these evaluations, the areas under the disease progress curve for each line were calculated, and individual and joint analyses of variance were performed. There is genetic variability among the corn genotypes for reaction to bacterial leaf streak, with a significant effect for the areas under the disease progress curve for incidence (AUDPCI) and severity (AUDPCS) between genotypes and between growing seasons, and for the genotype x season interaction. Lines LV1 and L14 are possible source genotypes for genetic resistance to the bacterial leaf streak.

Exploring the Relationship Between Pattern-Triggered Immunity and Quantitative Resistance to Xanthomonas vasicola pv. vasculorum in Maize.

Bacterial leaf streak (BLS) of maize is an emerging foliar disease of maize in the Americas. It is caused by the gram-negative nonvascular bacterium Xanthomonas vasicola pv. vasculorum. There are no chemical controls available for BLS, and thus, host resistance is crucial for managing X. vasicola pv. vasculorum. The objective of this study was to examine the genetic determinants of resistance to X. vasicola pv. vasculorum in maize, as well as the relationship between other defense-related traits and BLS resistance. Specifically, we examined the correlations among BLS severity, severity for three fungal diseases, flg-22 response, hypersensitive response, and auricle color. We conducted quantitative trait locus (QTL) mapping for X. vasicola pv. vasculorum resistance using the maize recombinant inbred line population Z003 (B73×CML228). We detected three QTLs for BLS resistance. In addition to the disease resistance QTL, we detected a single QTL for auricle color. We observed significant, yet weak, correlations among BLS severity, levels of pattern-triggered immunity response and leaf flecking. These results will be useful for understanding resistance to X. vasicola pv. vasculorum and mitigating the impact of BLS on maize yields.

Surface coatings based on chitosan and tannins applied in the in vivo prevention of corn streak disease

The bacterial corn streak disease, caused by Xanthomonas vasicola pv. vasculorum (Xvv) has emerged as a threat to corn production due to its rapid spread and resistance to conventional agrochemicals. Therefore, this study proposes polymeric surface coatings based on chitosan (CS) and tannins (TN) as antimicrobial agents against Xvv. The coatings were formed via the layer-by-layer (LbL) approach on oxidized polystyrene (PS). The coatings increased the wettability and roughness of the surfaces. In vitro assays measuring the minimum inhibitory and minimum bactericidal concentrations (MIC and MBC) demonstrated the antimicrobial activity of CS and TN. Coatings deposited on PS exhibited in vitro anti-adhesive properties against Xvv. The in vitro antimicrobial results were compared with control assays performed with an ionic liquid (IL). The IL was also associated with the polymeric coatings. Polymeric coatings, with or without IL, were deposited on corn leaves for in vivo assays. The IL had no activity against Xvv, and its presence in the CS solution seemed to impair the coating deposition on the corn leaves. However, the in vivo assays confirmed the protective efficacy of the polymeric coatings against Xvv infection, acting as physical barriers. The surface coatings also significantly reduced the Xvv symptoms in infected plants even after the disease spread. These outcomes were attributed to the film-forming ability of CS and TN polymers, the coatings' antimicrobial action, and the LbL efficiency in depositing the coatings on the corn leaves. This study introduces a promising environmentally and economically viable strategy for combating bacterial corn streak disease using biodegradable, cytocompatible natural polymers. The surface coatings offer a sustainable method to address bacterial corn disease, overcoming the limitations of agrochemicals.

Responses of common enset (Ensete ventricosum) varieties in Ethiopia to Xanthomonas and virulence of Xanthomonas strains

Enset is a vital food crop for over 20% of the population living in Ethiopia. Enset bacterial wilt (EBW) disease caused by a pathogen Xanthomonas vasicola pv. Musacearum (Xvm) is among the challenges for its production. This study evaluated the tolerance level of enset varieties in Gamo highland against Xvm. During the field survey, EBW infected enset samples were collected for isolating and characterizing Xanthomonas responsible for causing EBW disease. The isolates were used for infecting different enset varieties in the field. Soil samples were also collected from the farm before enset cultivation (F-BC), during enset cultivation (F-DC), and after EBW disease development (F-AD). Among 126 bacterial isolates, 18 Xvm were found to yield amplicons at 420 bp using Xcm-36 as a specific primer. During pathogenicity tests, all Xvm isolates caused EBW disease before 38 days in the Bodha enset variety. Except for the variety Maze, all the field-tested varieties began to show a typical wilt symptom after 45 days of infected enset cultivation. Isolate X-D5 showed a significantly (P ≤ 0.05) higher virulent capacity to all enset varieties tested than isolates X–B4 and X–K4. Overall, findings of the fieldwork provide clues on the traditional knowledge of characterizing different enset varieties for susceptibility and tolerance to Xvm that can be useful in designing EBW disease management strategies.

First report of Klebsiella Leaf Streak on Sorghum Caused by Klebsiella variicola in Haryana, India.

Sorghum (Sorghum bicolor [L.] Moench) is one of the top ten cereal crops in the world and is grown for fodder and seed purposes. During the fall of 2019 to 2022, a disease causing small to long streaks on leaves was observed in sorghum fields of Hisar (29° 9' 6.6996'' N, 75° 43' 16.0428'' E), Rohtak (28° 53' 43.8540'' N, 76° 36' 23.8068'' E) and Mohindergarh (28° 16' 6.0492'' N, 76° 9' 3.3552'' E) regions of Haryana between July and October. The reddish brown streaks were observed in the interveinal spaces of upper and lower leaves. The disease incidence reached 20-30% of plants in affected fields. The diseased leaf tissues were disinfected with 70% alcohol and placed in a tube with sterile water. After 30 minutes, 100 µl of the suspension was inoculated onto nutrient agar medium, incubated at 28 ± 2°C for three days, and a pure culture was obtained by restreaking on nutrient agar (Janse, 2005). The rod-shaped gram-negative bacterium with round, cream to white colonies was positive for methyl red, citrate utilization, urease activity, and glucose, lactose, sorbitol, rhamnose and sucrose fermentation tests. The genomic DNA of the bacterial suspension was extracted and 16S rDNA was amplified using universal 27F/1492R primers (Marchesi et al. 1998), resulting in tentative identification as Klebsiella sp. It was further confirmed with PCR amplification of Klebsiella specific primers (F:5'-CGCGTACTATACGCCATGAACGTA-3'; R:5'-ACCGTTGATCACTTCGGTCAGG-3') for gyrA gene (Brisse and Verhoef 2001). Discrete PCR amplicons of 1,500 (16S rDNA) and 300 bp (gyrA) were observed in a 1% (w/v) agarose gel. Forward and reverse DNA sequencing of both amplicons of the Hisar isolate (VMKV101) was carried out using a BDT v3.1 Cycle sequencing kit and consensus sequences were generated by using the program SeqMan Ultra (DNASTAR Lasergene). Sequences of the PCR products were deposited in GenBank with accession numbers MZ569433 (16S rDNA) and OP390080 (gyrA). The 16S rDNA sequence was 97.32% similar to K. variicola strain 13450 (CP026013; 1,450/1,490 bp) and the gyrA sequence had 99.66% similarity to K. variicola strain FH-1 (CP054254; 297/298 bp). A 16S RNA-based phylogenetic tree done by MEGA11 (Tamura et al. 2021) using the Maximum Likelihood method showed that strain VMKV101 clustered with K. variicola type strain F2R9. The complete bacterial genome (GCA025629215), sequenced by the Ion GeneStudio S5 system using Ion 530 chips (Thermo Fisher Scientific), was 99.03% identical by average nucleotide identity (ANI) to the type genome (CP045783) of Klebsiella variicola, with 87.8% genome coverage. For pathogenicity testing, a bacterial suspension (10 ml, 1×107 colony forming units/ml) was injected into the whole whorl after mechanical injury on 15-20 days old seedlings of the susceptible genotype HC-171, then plants were incubated at 35 ± 2°C, >80% relative humidity. Control plants were injected with sterile distilled water. Initial symptoms were observed on leaves of inoculated plants after 5 to 7 days as narrow, small longitudinal reddish brown streaks. As the disease progressed, the streaks on the leaf blade increased in number and size maintaining the reddish brown color. These streaks had slightly wavy margins and were surrounded by bright yellow halos. After 15 to 20 days, the streaks were 0.5 to 2.0 mm wide and 1.0 to 5.0 cm long, occasionally up to 10.0 cm long on both side of the leaves. Over time, neighboring streaks coalesced to form large necrotic areas. All inoculated plants exhibited identical symptoms. No symptoms were observed on control leaves. The reisolated bacterium from diseased sorghum leaves showed exactly the same morphological, biochemical and 16S RNA and gyrA molecular characteristics. To our knowledge, this is the first report of K. variicola causing a leaf streak disease on sorghum. Klebsiella species primarily cause diseases in humans and animals, but K. variicola has been found to incite banana soft rot (Fan et al. 2015) and K. aerogenes to cause stem rot in pearl millet (Malik et al. 2022). Differences of prevalence, spread and control between K. variicola and two other bacteria (Xanthomonas vasicola pv. holcicola causing Bacterial leaf streak; Paraburkholderia andropogonis causing Bacterial leaf stripe) causing leaf streak diseases on sorghum need to be determined. The identification of Klebsiella leaf streak disease lays the groundwork for future investigations into epidemiology and management of K. variicola on sorghum.

Changing Dynamics in the Spread and Management of Banana Xanthomonas Wilt Disease in Uganda Over Two Decades

Banana Xanthomonas wilt (BXW) is a destructive disease caused by Xanthomonas vasicola pv . musacearum ( Xvm), a bacterium that indiscriminately infects all banana varieties grown in East and Central Africa (ECA). In this region, BXW was first reported in 2001 in Uganda and was projected to eliminate >90% of Uganda's banana crops (worth USD4 billion) if not controlled in less than 10 years. Lack of basic information led to application of control approaches that were based on similarity of BXW symptoms to those of Moko disease of banana. However, the approaches were unsuccessful and, in 7 to 9 years, BXW had covered six countries and threatened to wipe out the banana industry in ECA. However, BXW has been tamed to date, mainly due to relentless and systematic deployment of carefully crafted and packaged cultural control practices based on epidemiological information generated within target banana cropping ecosystems. In Uganda, the initial “top-down” communication approaches reached >85% of banana farming communities but did not mobilize the communities enough into action; hence, only 30% impact in controlling BXW was registered. In contrast, participatory approaches mobilized farming communities into action and effectively controlled BXW at field and community levels to near eradication. The approaches effectively controlled BXW in Uganda and, consequently, in eastern Kenya, northern Tanzania, Rwanda, Burundi, and the Democratic Republic of Congo. This article reviews step-wise processes leading to success over the 2 decades and identifies critical research gaps. Deployment of resistant genotypes is urgently needed as a significant addition to the BXW management toolbox to create BXW-free banana cropping systems in ECA. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Bacterium-enabled transient gene activation by artificial transcription factors for resolving gene regulation in maize.

Understanding gene regulatory networks is essential to elucidate developmental processes and environmental responses. Here, we studied regulation of a maize (Zea mays) transcription factor gene using designer transcription activator-like effectors (dTALes), which are synthetic Type III TALes of the bacterial genus Xanthomonas and serve as inducers of disease susceptibility gene transcription in host cells. The maize pathogen Xanthomonas vasicola pv. vasculorum was used to introduce 2 independent dTALes into maize cells to induced expression of the gene glossy3 (gl3), which encodes a MYB transcription factor involved in biosynthesis of cuticular wax. RNA-seq analysis of leaf samples identified, in addition to gl3, 146 genes altered in expression by the 2 dTALes. Nine of the 10 genes known to be involved in cuticular wax biosynthesis were upregulated by at least 1 of the 2 dTALes. A gene previously unknown to be associated with gl3, Zm00001d017418, which encodes aldehyde dehydrogenase, was also expressed in a dTALe-dependent manner. A chemically induced mutant and a CRISPR-Cas9 mutant of Zm00001d017418 both exhibited glossy leaf phenotypes, indicating that Zm00001d017418 is involved in biosynthesis of cuticular waxes. Bacterial protein delivery of dTALes proved to be a straightforward and practical approach for the analysis and discovery of pathway-specific genes in maize.

VIRULENCE OF PSEUDOMONAS SYRINGAE STRAINS FROM SORIZ (SORGHUM ORYSOIDUM) AND THEIR SPECIALIZATION

Objective. To study the virulence properties of Pseudomonas syringae strains isolated from soriz and various representatives of sorghum crops in Ukraine and to establish the sensitivity range of plants to these pathogens. Methods. Ten strains freshly isolated from soriz (Sorghum orysoidum) were used to study virulence properties, namely: Pseudomonas syringae 210342, 211141a, 211141, 210341, 21034, 210541b, 210541, and Pseudomonas sp. 210521, 21052, 21054, pathogenic strains of sorghum crops from the collection of the Department of Phytopathogenic Bacteria of D. K. Zabolotny Institute of Microbiology and Virology of the National Academy of Sciences of Ukraine and collection strains of phytopathogens that can be potential causative agents of bacterial diseases of soriz or are causative agents of diseases of agricultural crops that can be used in crop rotation. The virulence properties of strains isolated from sorghum were determined on plants of the genus Sorghum. To establish the range of crops sensitive to these pathogens, a number of plants belonging to other genera and families, both cultivated and weed, were tested. Artificial inoculation was carried out in the greenhouse and in the field as injection of bacterial suspension of 1×109 CFU/mL into the leaf surface and stem at all phases of the development of soriz and sorghum cultures. Accounting for artificial contamination was carried out in 7 to 14 days using a locally modified 6-point scale. Aggressiveness of bacteria was assessed by the size of necrosis that formed at the site of injection of the bacterial suspension. Aggressiveness was calculated as the arithmetic mean of the results. Results. P. syringae strains isolated from soriz were found to be virulent for soriz and sorghum crops, however, heterogeneous in aggressiveness. The most aggressive strains were P. syringae 211141a, 210341, and 21034. Some collection strains, isolated from different cultures, showed higher aggressiveness against sugar and grain sorghum than against soriz and Sudan grass. The studied strains of phytopathogens were found to affect segetal vegetation; the most sensitive to the studied strains were horsetail, field bindweed, goldenrod. They showed high aggressiveness against setaria, ragweed, and common sedge. Strains of P. syringae affecting potato, beet, sunflower and tomato plants were identified. Conclusion. Pseudomonas syringae strains isolated from contaminated sorghum plants are virulent and capable of infecting a wide range of plants, including plants of the sorghum family, other types of agricultural crops, and various types of segetal vegetation. Strains of Pectobacterium carotovorum, Xanthomonas vasicola pv. holcicola, Diskeya chryzanthemy, Pantoea agglomerans can be potential pathogens of sorghum crops. The results indicate that segetal vegetation can serve as a reservoir of bacterial infections and play a role in the transfer of bacterial pathogens.

New Insights on Alternative Hosts of Xanthomonas vasicola pv. vasculorum, the Causal Agent of Bacterial Leaf Streak of Maize

Bacterial leaf streak (BLS) of maize (Zea mays), caused by the bacterium Xanthomonas vasicola pv. vasculorum (Xvv), was first reported in Brazil in 2018. In this study, we evaluated 52 species of cultivated plants, cover crops, forage, and grasses that are used in succession or crop rotation with maize, and weeds with natural occurrence in maize-producing regions, to determine their potentials as alternative hosts for Xvv. We investigated (i) the pathogenicity of Xvv based on symptom development, (ii) epiphytic colonization of the bacterium in asymptomatic plants, and (iii) bacterial colonization in plant tissues using scanning electron microscopy (SEM) in symptomatic and asymptomatic species. Ten species, all belonging to the Poaceae family, presented symptoms after Xvv infection, including Avena sativa (cvs. IPR Afrodite and IPR Esmeralda), A. strigosa (cv. IPR 161), Hordeum vulgare (cv. BRS Cauê), Oryza sativa (cv. IPR 117), Brachiaria brizantha (Brizantha and cv. Marandu), Digitaria horizontalis, D. insularis, Echinochloa colonum, Eleusine indica, and Sorghum arundinaceum. Furthermore, epiphytic colonization by Xvv was observed in 23 asymptomatic species. Scanning micrographs revealed that Xvv cells and their aggregates were distributed throughout the leaf surface. In addition, bacterial colonization in the intercellular tissues of the substomatal chambers of white oat, black oat, and maize was observed across the tissue fractures. Despite showing typical symptoms of Xvv infection, SEM examination revealed evidence of Xvv colonization only on the leaf surface of rice. In asymptomatic species, such as rye, sorghum, and millet, a low number of bacterial cells were found on the leaf surface. However, no evidence of internal tissue colonization was observed in millet fractures, suggesting that Xvv survives only epiphytically in this species.

Genome‐wide association study for bacterial leaf streak resistance in maize

AbstractMaize (Zea mays L.), one of the most important crops worldwide, is affected by foliar diseases that limit its global production. Bacterial diseases have increased in Argentina during the last years. The aim of this work was to explore a maize panel provided by the International Maize and Wheat Improvement Center (CIMMYT) to identify alleles associated with resistance to bacterial leaf streak (BLS) of maize, a disease caused by Xanthomonas vasicola pv. vasculorum, in central Argentina. A diverse panel of 200 maize lines was evaluated for resistance to bacterial diseases in four environments of central Argentina in 2020 and 2021. The predictor of the genetic merit does not include environmental effects and 46,990 single‐nucleotide polymorphisms obtained by genotyping‐by‐sequencing were used in the genome‐wide association study (GWAS). The 10 lines with the lowest severity across environments belonged to different environmental adaptation programs defined by CIMMYT. The GWAS allowed us to identify 11 genomic regions associated with BLS, located in chromosomes 1, 2, 5, 7, 8, and 9. Five of those regions, located in bins 1.04, 2.01, 5.03, 8.06, and 9.03, were associated with plant defense candidate genes such as strictosidine synthase‐like 11, protein‐serine/threonine phosphatase, and a putative Leucine‐Rich repeats receptor‐like serine/threonine‐protein kinase gene. Our study provides potential resistance alleles to BLS that can be incorporated to improve maize breeding programs.

Characterization of a foxtail mosaic virus vector for gene silencing and analysis of innate immune responses in Sorghum bicolor.

Sorghum is vulnerable to many biotic and abiotic stresses, which cause considerable yield losses globally. Efforts to genetically characterize beneficial sorghum traits, including disease resistance, plant architecture, and tolerance to abiotic stresses, are ongoing. One challenge faced by sorghum researchers is its recalcitrance to transformation, which has slowed gene validation efforts and utilization for cultivar development. Here, we characterize the use of a foxtail mosaic virus (FoMV) vector for virus-induced gene silencing (VIGS) by targeting two previously tested marker genes: phytoene desaturase (PDS) and ubiquitin (Ub). We additionally demonstrate VIGS of a subgroup of receptor-like cytoplasmic kinases (RLCKs) and report the role of these genes as positive regulators of early defence signalling. Silencing of subgroup 8 RLCKs also resulted in higher susceptibility to the bacterial pathogens Pseudomonas syringae pv. syringae (B728a) and Xanthomonas vasicola pv. holcicola, demonstrating the role of these genes in host defence against bacterial pathogens. Together, this work highlights the utility of FoMV-induced gene silencing in the characterization of genes mediating defence responses in sorghum. Moreover, FoMV was able to systemically infect six diverse sorghum genotypes with high efficiency at optimal temperatures for sorghum growth and therefore could be extrapolated to study additional traits of economic importance.

In vitro sensitivity of Xanthomonas vasicola pv. vasculorum and the control of bacterial leaf streak of corn with copper oxychloride alone and in mixtures with mancozeb and fluxapyroxad

In vitro sensitivity of Xanthomonas vasicola pv. vasculorum and the control of bacterial leaf streak of corn with copper oxychloride alone and in mixtures with mancozeb and fluxapyroxad

Spread of Xanthomonas vasicola pv. musacearum within banana mats: implications for Xanthomonas wilt management

Xanthomonas wilt (XW) of banana caused by Xanthomonas vasicola pv. musacearum (Xvm) does not spread to all plants physically interconnected through the rhizome when one or a few are diseased. Factors causing this incomplete systemic spread of Xvm are not fully known yet could be important for XW management. We explored the effect of 1) Xvm inoculum amounts; 2) number, size, and position of suckers on mother plant corms; and 3) other mother plant attributes on sucker colonization. A shorter (p < 0.05) incubation period (17.9 vs 21.1 days) and higher (p < .001) cumulative number of symptomatic leaves (5.2 vs 1.6 leaves) was observed when all leaves compared to only two leaves were inoculated. Xvm was recovered in corms at 29 days post inoculation (dpi) in both treatments with no differences (p > 0.05) in proportions of corms with Xvm between the treatments. However, Xvm was recovered earlier and at a higher frequency in attached suckers when all leaves were inoculated. Lower Xvm recoveries occurred in the lower corm sections to which most suckers were attached relative to the middle and upper corm sections. Xvm incidence in corms increased with the number of attached maiden suckers, and the dpi, while it declined with increasing mother plant pseudostem and corm height. Thus, Xvm spread within mats is influenced by the amount of inoculum and the physiological stage of the mother plant and attached suckers. The position of suckers, predominantly at the bottom of corms also protects them from infection. Measures that reduce Xvm inoculum build-up in mats will thus minimize within mat Xvm spread.